The present invention relates to charge display circuits for motor vehicles, and more particularly, to a charge display circuit of which the power consumption is reduced.
A conventional charge display circuit is shown in FIG. 1. In the circuit of FIG. 1, a charging generator 1 includes an AC generator having three-phase output windings 2 and a field winding 3, and a full-wave rectifier circuit including a rectifier 4, a first rectifier output terminal 5, a second rectifier output terminal and an AC input terminal 7. In FIG. 1, reference numeral 8 designates a charge display lamp; 9, a key switch; 10, a resistor through which current flows for turning on the charge display lamp; 11, a regulator; and E, a battery.
When the key switch 9 is closed, current flows from the battery E through the charge display lamp 8 and the resistor 10 so that the charge display lamp 8 is turned on. When the engine (not shown) starts to drive the charging generator 1, a voltage is developed at the second rectifier output terminal 6 so that the voltages at the two terminals of the charge display lamp 8 become equal. As a result, the charge display lamp 8 is turned off, and a larger current flows in the resistor 10.
When the generation of electricity is suspended, for instance, because the field winding is broken during the operation of the engine, no voltage is provided at the second rectifier output terminal 6. Accordingly, current again flows from the battery E through the charge display lamp 8 to the resistor 10 so that the charge display lamp 8 is turned on, thus indicating the fault in the field winding 3. That is, the resistor 10 serves as a resistor for detecting faults in the field circuit.
However, the above-described conventional circuit is disadvantageous in that, if the resistance of the resistor 10 is decreased, the brightness of the charge display lamp 8 is increased, but the amount of current flowing in the resistor 10 is increased, thus increasing the loss of electric power. If, on the other hand, the resistance of the resistor 10 is increased, the loss of electric power is decreased, but the brightness of the charge display lamp 8 is decreased.